The invention relates to electrical closing systems and, in particular, to a trapping prevention function for electric window winders and vehicle roofs.
In electrical closing systems, for example electric window winders or roof systems in a motor vehicle, a closing part, for example a window pane or a moving vehicle roof, in vehicles can be electrically opened or closed, with an electric motor being used for moving the closing part. A closing process of the closing part is automatically monitored with the aid of a so-called trapping prevention function. In this case, trapping of an object between the moving closing part and stationary elements, for example a window frame, has to be identified before the trapping force exerted on the object by the electric motor via the window exceeds a determined value. The trapping prevention function is specified in the statutory regulations FWVSS 118 (S5) in the USA and 74/60/EEC (5.8.3) in the EU, with the maximum trapping force being defined as 100 N.
Electric window winders and roof systems are generally operated by an operator control element. An electric motor is driven by operation of the operator control element, with the window or the roof being opened or closed as a function of the direction of rotation of the electric motor. In order to implement the trapping prevention function, the current and/or the rotation speed of the DC motor are usually evaluated in a corresponding control unit, this allowing cost-effective implementation of said function.
EP 0 865 137 A1 discloses a method for controlling the closing process of closing devices in the case of at least one part which is moved by electric motor, with a trapping prevention function being activated in the start-up phase as a function of the profile, which is dependent on the closing travel, of at least one characteristic motor variable when a closing travel-dependent activation value is reached.
EP 1 168 559 A1 discloses that, in the case of an automatic window winder, identifying an object which forms an obstruction using a profile of a rotation speed and accordingly triggering a trapping prevention function so that the force on the object is limited.
It is difficult to comply with the statutory requirements during start-up of a motor since the characteristic motor variables, for example the motor rotation speed and the motor current, can vary considerably as a function of the degree of drive play, the change in friction over the service life of the closing system and the position of the closing part. However, the reaction rate during start-up of a motor plays a crucial role. Furthermore, the drive play must not have any effect on the time for activating the trapping prevention function during start-up of the electric motor which drives the closing mechanism.
Basically, it is necessary, in the case of an electric window winder, to activate the trapping prevention function as quickly as possible after operation of the operator control element, so that trapping can be identified as far as possible without a dangerous delay. On account of the considerable variation in the characteristic motor variables which occurs particularly during start-up of the motor, it is not possible to activate the trapping prevention function at the same time as the operator control element is operated in order to activate the window winder since instances of incorrect identification cannot be precluded.